This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Increasingly, mobile radio handsets incorporate multiple radios that operate over different protocols and different frequency bands. For example, it is typical that a new mobile handset is equipped with one or more of a global positioning system GPS receiver, a Bluetooth transceiver, a wireless local area network WLAN transceiver, and a traditional FM radio receiver. More prevalent currently in Europe and Asia than in the US, some mobile handsets also incorporate a radiofrequency identification RFID transceiver, which is often used for mobile electronic commerce when linked to a credit/debit card, for electronic keys (car, house, etc.), and/or for reading a passive RFID tag (e.g., interactive advertising). RFID has a viable signal range of about 10 centimeters and operates in the 13.56 MHz frequency band. All of these radios above can generally be considered as secondary radios, in contrast to a cellular transceiver which may be considered the primary radio of a mobile telephony handset. Note also that it is common for such handsets to have multiple primary radios (e.g., tri-band or quad-band) for communicating on different cellular protocols such as GSM (global system for mobile communications, or 3G), UTRAN (universal mobile telecommunications system terrestrial radio access network, or 3.5G), WCDMA (wideband code division multiple access), OFDMA (orthogonal frequency division multiple access), to name but a few examples.
Each of these radios must operate with an antenna tuned to the requisite frequency band. Typically, near-field communications (NFC, a regime in which RFID is a member), Bluetooth, WLAN, and GPS are implemented with separate antennas. Where the handset also includes an internal FM radio, typically there is also an internal FM receiver including antenna (FM-RX) and an internal FM transmitter with an antenna (FM-TX) that may be separate from the FM-RX antenna.
All of this hardware of course must be fit into a handheld-size package, of which the housing itself must either facilitate the proper antenna resonances or not interfere with such proper resonances. This problem of space is increasingly acute considering the current trend toward metallic handset housings/covers/casings as compared to plastic which was recently the most common material for mobile phone housings. Often in past handset layouts there was a separate antenna for Bluetooth and WLAN, for GPS, for NFC, and for FM radio (broadcast), as well as for the primary cellular radio(s). While the Bluetooth, WLAN and GPS antennas can be made quite small, the FM antenna(s) require much more space, particularly if they are implemented separately for receive RX and transmit TX events.
Specific implementations for multiplexing multiple radios into a single antenna are detailed at U.S. Pat. Nos. 6,950,410 and 7,376,440. Peter Lindberg and Andrei Kaikkonen describe, at an Internet publication entitled “BUILT-IN HANDSET ANTENNAS ENABLE FM TRANSCEIVERS IN MOBILE PHONES” (July, 2007), a FM transceiver antenna designed for a handset that is a single turn half-loop, shorted at one end and connected at the other to a co-designed preamplifier which also has a shunt capacitor for ac shorting at GSM frequencies.